1. Field of the Invention
This invention relates to improvements in a method of operating a metal-halogen battery such as a zinc-bromine battery, and more particularly to a technique for preventing a dendrite from formation during changing the battery.
2. Description of the Prior Art
A metal-halogen battery such as a zinc-bromine battery includes a plurality of cells which are electrically connected in series with each other in order to generate a high voltage to be picked up. The respective cells are separated from each other by separator plates. Each cell includes a bipolar electrode plate which defines positive and negative electrode chambers on the opposite sides thereof. Two kinds of electrolyte solutions are respectively circulated through the positive and negative electrode chambers under the action of pumps thereby to accomplish charging and discharging the battery.
In such a zinc-bromine battery, metallic zinc is electrodeposited on the surface of the negative electrode during the charging while the electrodeposited metallic zinc is dissolved in the electrolyte solution during the discharging, thus developing an electromotive force. It is known that the electrodeposition of zinc takes the form of a dendrite, which has considerably shortens a battery service life. In order to improve such shortening of the battery service life due to the dendrite, a variety of countermeasures have been hitherto taken. For example, inhibitors are added to the electrolyte solutions; or a complete discharging is once carried out in one charging and discharging cycle in order to electrically remove the electrodeposited zinc.
However, difficulties have been encountered in such dendrite prevention measures. Concerning addition of the inhibitors, if organic inhibitors are employed, they are short in life and therefore cannot provide a stable dendrite formation preventing effect throughout a long period of time. If inorganic inhibitors are used, they can suppress the formation of dendrite upon forming a codeposition between them and zinc; however, they forms a segregation so that the dendrite formation suppressing effect is unstable throughout a long period of time. Concerning carrying out the complete discharging, it needs several hours and is unavoidably required in each charging and discharging cycle. This is very inconvenient and requires a device for causing the complete discharging.